In order for robots to effectively perform increasingly more delicate and detailed tasks, it becomes necessary to provide sensory apparatus such as in the hand of the robot, which is functionally equivalent to the various sensors which human workers are naturally endowed, for example, touch. Touch is of particular importance for the tasks such as close-up assembly work, where vision may be obscured by arms or other objects and for providing sensory feedback necessary for gripping delicate objects firmly without causing damage or slippage. Touch can also provide a useful means for discriminating between objects having different sizes, shapes or weights and to determine their orientation.
Tactile sensors have been developed for use with industrial robots. Typically, the tactile sensors currently suggested for use today comprise a printed circuit board or the like as a base, and elastomeric skins embodying conductive elements, piezoelectric elastomers and skins laced with semiconductive coils. The prior art is represented in the following publications: "Compliant Tactile Sensor Pad System", Barry Wright Corporation, published June 1983; "Integrated Tactile Sensor for Robots", NASA Tech Briefs, Winter, 1983; and IBM technical disclosure bulletin, volume 19, no. 2, July 1976; USSR Pat. No. 816,963, and U.S. Pat. No. 4,001,556.
The skins having the desired electrical properties typically suffer in other physical and chemical properties such as a loss of elasticity and/or a loss of chemical inertness. Further, these skins because of the incorporation of the electrical characteristics have increased hysteresis (the phenomena where the output versus load from a tactile sensor being loaded is different from the output versus load when the tactile sensor is being unloaded). Abrasions or cuts or wear to the prior art skins affect their sensing ability in that the abrasion or cut will affect the electrical characteristics incorporated in the skin.
An additional drawback of some prior art tactile sensors is that they are point sensors and, thus, whole areas of the sensor are unable to sense touch. Further, where the prior art sensors are used in the presence of electromagnetic radiation, erroneous signals are created which are reported by the sensor. A further difficulty with some prior art sensors is that they experience cross-talk, which reduces the effective resolution. Resolution is the number of sensing elements per unit area. Cross-talk is the phenomena where sensing elements are falsely activated by activated neighboring elements. Cross-talk results from both the internal wiring of prior art devices and the skin-support interaction. Cross-talk due to internal wiring type sensors is caused by the signal being received and conducted along extraneous paths. Mechanical cross-talk is caused by nonlocalized stress and a sensing skin.
My invention overcomes these prior art problems and provides a high resolution sensor substantially free of cross-talk, which increases substantially the sensing area available to respond to touch. The skin of my sensor does not incorporate any electrical components therein and, thus, may be selected based solely on physical and chemical properties.
Broadly, my invention comprises a tactile sensor wherein a plurality of members are received in a housing. The members are arrayed in a grid-like configuration to define sensing regions in a side-by-side relationship. The sensing regions are electrically isolated from one another. A pressure sensitive skin is secured to the housing and is in communication with the sensing regions. Means are disposed in the housing and in communication with the sensing regions to provide an output in response to a deflection in the skin where the sensing region exists. The sensor does not measure deflection associated directly with the object contact. The sensor measures the compressive stress on the under side of the skin.